How to solve pls help me...

Electricity and Magnetism Level 3

A Circular wire containing a magnetic field B at his center. The coil is now rewound so as to have 3 turns and the same current 'i' passes through it. The new magnetic field at his center is...

3B B/3 9B B/9

Anamaya Sharma by Anamaya Sharma , 27, India

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2 solutions

Harsh Peswani
Oct 4, 2014

B=nuI/2r As the same wire is wounded 3 times so therefore radius will become r/3 times so putting in formula we get B1=9nuI/2r=9b

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Anamaya Sharma
Aug 20, 2014

Idk how the answer is coming pls tell the solution to me!!!

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The volume of the coil has to remain constant, so when we increase the number of turns, the circumference (the radius) of the circle coil will decrease by the same rate. As the number of turns will increase by three times, the radius will be decreased to its third and as we know that B = N I u 2 r B= \frac{NIu}{2r} then the new magnetic flux density will equal 3 N I u 2 r 3 \frac{3NIu}{\frac{2r}{3}} which equals 9 B . \boxed{9B.}

Norhan Mahmoud - 6 years, 6 months ago

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What does the letter (u) mean? ,, i think the rule is B = N I μ 0 2 r B=\frac { NI{ \mu }_{ 0 } }{ 2r }

Abdulrahman El Shafei - 6 years, 6 months ago

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I meant by u the permeability but I didn't know how to type its symbol. Sorry about that.

Norhan Mahmoud - 6 years, 6 months ago

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@Norhan Mahmoud – u can use Daum equation editor

Abdulrahman El Shafei - 6 years, 6 months ago

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